<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Smooth 12-Second Sky Gradient Animation</title>
  <style>
    body, html {
      margin: 0;
      padding: 0;
      height: 100%;
      width: 100%;
      overflow: hidden;
    }
    .gradient-container {
      position: fixed;
      top: 0;
      left: 0;
      width: 100%;
      height: 100%;
    }
    .gradient-layer {
      position: absolute;
      top: 0;
      left: 0;
      width: 100%;
      height: 100%;
      mix-blend-mode: screen;
    }
    #layer1 { animation: gradient1 12s infinite; }
    #layer2 { animation: gradient2 12s infinite; }
    #layer3 { animation: gradient3 12s infinite; }

    @keyframes gradient1 {
      0%, 100% { background: #00000c; }
      25% { background: #020111; }
      50% { background: #20202c; }
      75% { background: #40405c; }
    }
    @keyframes gradient2 {
      0%, 100% { background: #00000c; }
      25% { background: #191621; }
      50% { background: #515175; }
      75% { background: #6f71aa; }
    }
    @keyframes gradient3 {
      0%, 100% { background: #00000c; }
      25% { background: #3a3a52; }
      50% { background: #8a76ab; }
      75% { background: #b1b5ea; }
    }
  </style>
</head>
<body>
<div class="gradient-container">
  <div class="gradient-layer" id="layer1"></div>
  <div class="gradient-layer" id="layer2"></div>
  <div class="gradient-layer" id="layer3"></div>
</div>
</body>
</html>